Small characteristic use particles, i.e., particles having an average diameter of less than about 15 μm (microns), have been used in numerous applications to impart certain desirable characteristics to a target medium. Target medium, as used herein, means any liquid, semi-solid or solid medium to which the characteristic use particle is added. Characteristic use particle, as used herein, means a particle of a material that confers a desired benefit. For example, small amounts (e.g., about 1 to 2% by weight) of powdered or small particle size polytetrafluoroethylene (PTFE) have been incorporated in a variety of compositions to provide the following favorable and beneficial characteristics: (i) in inks, PTFE provides excellent mar and rub resistance characteristics; (ii) in cosmetics, PTFE provides a silky feel; (iii) in sunscreens, PTFE provides increased UV shielding or SPF (sun protection factor); (iv) in greases and oils, PTFE provides superior lubrication; and (v) in coatings and thermoplastics, PTFE improves abrasion resistance, chemical resistance, weather resistance, water resistance, and film hardness.
Without wanting to be limited by any one theory, it is believed that these small characteristic use particles are able to impart their desirable characteristics as a result of the unique chemical properties of the materials of which they are comprised. Unfortunately, those same unique chemical properties typically cause the particles to agglomerate or self associate. Additionally, when the characteristic use particles are placed in chemically distinct media, such as a hydrophobic characteristic use particle in a hydrophillic medium, agglomeration or self-association is well known to occur. Characteristic use particles are, therefore, typically difficult to disperse and stabilize. For example, it is well known that PTFE is very difficult to disperse and stabilize (i.e., suspend) in target fluid systems (e.g., water, oils, solvents, coatings, and inks) and target semi-solid or solid systems (e.g., polymers, plastics, nylon). As a result, special chemical additives referred to as compatibilizing agents (e.g., surfactants, wetting agents, surface treating agents, etc.) are typically employed to assist dispersion and/or suspension of these particles in the target fluid, semi-solid or solid system. In addition to added cost, these compatabilizing agents can cause deleterious effects or alter the performance of the target system in which they are incorporated. In general, the compatibilizing agents are molecules having (i) at least one portion that is a chemical group that strongly associates with, or the surface of, a characteristic use particle and (ii) at least one other portion that is a chemical group that associates with a target medium. They serve, therefore, to chemically alter the surface properties of the characteristic use particle by forming an intermediary phase between the self-associating material and the other chemicals in the target medium, typically through complex chemical interactions, such as covalent bonding, ionic interactions, hydrogen bonding, hydrophillic interactions, hydrophobic interactions, van der Waals interactions and the like. Thus, there is a need to develop new dispersion methods and compositions to eliminate the need for these compatibilizing agents that function via these complex chemical interactions.
It is, therefore, an object of the present invention to provide methods and compositions, which disperse self-associating materials in a target medium using less than the typical amounts of compatibilizing agents for the material being dispersed in the target medium. Thus, the instant compositions and methods do not rely solely on chemical interactions in order to prevent agglomeration.